Sweet Potato Extract May Treat Diabetes

March 10, 2004 -- An extract from white sweet potatoes may help prevent type 2 diabetes.

The product is Caiapo, sold in Japan and South Korea by the Japanese firm Fuji-Sangyo. It's made from the skin of white sweet potatoes grown in Japan's mountainous Kagawa Prefecture. Eaten raw, these sweet potatoes are a folk remedy for anemia, high blood pressure -- and diabetes.

Caiapo extract prevented diabetes in rat studies. Fuji-Sangyo funded human tests at the University of Vienna in Austria. The results of those studies, led by Bernhard Ludvik, MD, appear in the February issue of Diabetes Care.

Every morning, Ludvik gave two bulky Caiapo tablets -- or two equally bulky inert placebo pills -- to 61 people with type 2 diabetes who were treated with diet only. All study participants went on a weight-maintenance diet during the study. After three months, those who took Caiapo -- but not those taking placebo -- saw their HbA1C levels drop from 7.21 to 6.68. HbA1C indicates blood sugar levels during the past three months. People with diabetes are supposed to keep their HbA1C levels below 7.0.

"This is lowering HbA1C to a level which is almost normal," Ludvik tells WebMD. "This is comparable to any drug."

Ludvik says that five-month data show that those taking Caiapo continued to have lower HbA1C levels. What's happening, he says is that something in the extract is helping patients regain their sensitivity to insulin. Resistance to the action of insulin to lower blood glucose is one of the abnormalities seen in people with type 2 diabetes. It is also one of the early signs of type 2 diabetes.

"In my opinion, in this potato extract there seems to be some kind of insulin-sensitizing agent," Ludvik says.

In rat studies, Ludvik says, Caiapo has as strong an effect as glitazone drugs. Glitazones -- such as Avandia and Actos -- are potent insulin-sensitizing drugs.

Although he warns that long-term data are not available, Ludvik says he saw no side effects from Caiapo except for some very mild gastrointestinal upset in a few patients. None of them stopped treatment because of these side effects.

"I think it could be given to any patient with insulin resistance," Ludvik says. "We have not shown this in our clinical trials, but I think it would be very good in diabetes prevention."

Caiapo is not available outside of Japan and South Korea. However, it is advertised -- in Japanese -- on the Internet. White sweet potatoes are a common food, widely available as Cuban sweet potatoes or boniato. However, these are not exactly the same subtype of white sweet potato harvested in Japan.